Sex Safety and Personal Lubricants

Supplemental lubrication products for vaginal or anal intercourse represent a $219 million annual market in the US. But how safe are these products, those that are intended for direct use in the most sensitive parts of the body?

Last week, an article at Chemical & Engineering News (C&EN), the official organ of the American Chemical Society, delved into the chemistry and safety of these intimate use products.

Wolf says that the questions on lubricant safety comes from the fact that the FDA regulates these products as "medical devices" and not drugs. As such, safety testing is only required in pre-clinical animal models, not humans.

But a few lab-based studies have now shown that lubricants can damage the epithelial cells lining the vagina and rectum, with the potential increasing the risk of sexually-transmitted infectious diseases (STIs) ranging from HIV to Chlamydia. While direct prospective studies would be unethical, Wolf cites a recently-published epidemiology study by UCLA researchers associating consistent lubricant use for receptive anal intercourse with increased risk of exposure to Chlamydia, Neisseria gonorrhoeae, and syphilis.

The potential culprit in these products is their chemical characteristic called osmolality. The same chemicals that cause "slipperiness" cause water to be sucked out of the cells lining the vagina and rectum. Polyethylene glycol and glycerol are the typical compounds -- they reduce friction and also prevent water from evaporating, a process that would otherwise feel cold. Instead, these chemicals, glycerol in particular, have the potential for positive thermoception -- that is, they feel warmer when blown on. (Yes, lab folks, go pipet a bit of 10% glycerol on the back of your hand and blow.)

The C&EN team took three papers discussed by Wolf and created this graph for some common brands of personal lubricants.

The concern, though not explicitly proven, is that products with higher osmolality might poses more of a risk of tissue damage.

Wolf also notes another issue of concern: contraceptive lubricants that contain the spermicide, nonoxynol-9. This weak detergent kills spermatocytes essentially by poking holes in their outer membrane. Nonoxynol-9 was also originally thought to disrupt that capsid, or covering, of the HIV viral particle. But Wolf notes otherwise:

In 2002, however, a Phase II/III clinical trial of a nonoxynol-9 vaginal gel failed to protect women from HIV infection. Not only that, but the detergent actually increased the risk of HIV infection in the sex workers tested—women living in countries such as South Africa and Thailand who used the product three or four times per day (Lancet, DOI: 10.1016/s0140-6736(02)11079-8).

Nonoxynol-9 is also still used in some brands of condoms, also as a spermatocide.

In my lab days, I always wondered about the wisdom of using nonoxynol-9 as a spermatocide because we used to use a related compound, octoxynol-9 (better known to labbies as Triton X-100), to break open human epithelial cancer cells to examine the proteins inside them. But I had suspected that the contraceptive and lubricant industry had tested the concentrations of nonoxynol-9 they used to be selective cytotoxins to spermatocytes relative to vaginal epithelium.

Wolf has some other concerns about the antimicrobial products in some of these products because they can also disrupt the normal, helpful bacteria of the vagina. Species of Lactobacillus, for example, produces lactic acid that reacidifies the vaginal following male ejaculation of higher pH semen. Preventing the vagina from reacidifying could also predispose a woman to other bacteria and yeast infections.

What's needed -- and I hate to use the cliché -- is more research. This BMC Infectious Diseases paper cited by Wolf showed that mice instilled with various vaginal gels containing microbicide experienced greater herpes simplex-2 infections when challenged three days later. But the mouse vagina is not the human vagina. The US Centers for Disease Control and Prevention is currently testing some of these products in monkeys.

One major key to safety, regardless of whether one cares to use these products, to be in a monogamous sexual relationship where neither partner has an existing sexually-transmitted infection.

I'm a pharmacologist, freelance science and medicine writer, educator, and speaker with a passion for public understanding of science and medicine. I report on all things pharmaceutical and scientific from Durham, North Carolina, home of the Research Triangle Park.